Download Friend or foe of nutritional balance?

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SEPTEMBER
OCTOBER 2016
#32
THE MAGAZINE OF THE FRENCH NATIONAL
INSTITUTE OF HEALTH AND MEDICAL RESEARCH
Taste
Friend or foe
of nutritional
balance?
New
layout
Science&Santé new recipe: more reports, more portraits,
for more flavor and always more rigorous scientific news.
With an unchanged objective: to give you a "taste" of
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The Science&Santé editorial team
EDITORIAL
©Loïc Briand
Far more than a sensory
experience!
Loïc
Briand
am Leader
rception Te
Flavour Pe ciences du goût et
s
Centre des tion (Centre for the
ta
de l’alimen Taste & Diet), Inra, f
Sciences o Université de
CNRS,
, Dijon
Bourgogne
#32
September - October 2016
Subscription free, write to:
[email protected]
Inserm, 101, rue de Tolbiac
75654 Paris Cedex 13
www.inserm.fr
Taste is a chemical detection system that can evaluate the nutrient
content of food and signal the presence of toxic compounds. This
sense is very familiar to us and yet it is one of the most complex.
Our understanding of the physiological mechanisms underlying
gustatory function has progressed enormously in the last decade.
Moreover, new flavors have been developed, such as that of "umami"
or the taste of "fat", and the main receptors involved in tasting have
been identified. The sequencing of genomes has revealed genetic
differences that could affect taste perception and account for certain
dietary preferences.
Recent research has also revealed that receptors for sweetness can
be found in many organs and tissues, including the gut, pancreas,
adipose tissue, spermatozoa and the brain. Although the exact
physiological role of these receptors remains unelucidated, in the
gut they have been shown to be involved in regulating the absorption of glucose into the blood and in the release of hormones associated with satiety. These new roles are raising interest in the idea
of modulating this receptor with inhibitory compounds to control
diabetes or obesity.
And taste has not finished surprising us. In laboratories, scientists
and clinicians are continuing to advance our understanding of taste
perception which has not yet unveiled all its secrets.
Director of publication Yves Lévy Director of writing Arnaud Benedetti Editor-in-Chief Yann Cornillier Writing
Assistants Coralie Baud, Marie-Charlotte Ferran Headlines Julie Coquart Editorial Assistant Coralie Baud Collaborators
on this issue: Alice Bomboy, Françoise Dupuy Maury, Jean Fauquet, Caroline Guignot, François Maginiot, Stéphany Mocquery, Charles Muller,
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4
#32
#32
Grand angle
TASTE
Friend or foe of
nutritional balance?
piled by
Report com rrefixe
ie
P
n
Simo
Sweet or salty, acidic or bitter: taste lets us appreciate the flavors in all the foods
that we savor every day. For that reason, it plays an important role in regulating
what we eat by helping us to determine exactly what we are eating. Above and
beyond the nutritional aspect, taste is also a source of pleasure—a great deal of
pleasure. Sometimes taste drives our behavior patterns to such an extent that we
get sick. A paradox in the country of great cooking and good taste.
It is nevertheless possible to combine gustatory pleasure and health.
5
6
#32
Tongue
Salivary
glands
grand angle
Retronasal olfaction
Gustatory
nerve
A
Anatomy of
the caliciform papilla
Thalamus
Hypothalamus
Olfactory bulb
Hippocampus
Olfactory epithelium
Solitary nucleus
Nasal cavity
Orthonasal
olfaction
Tongue
Gustatory nerves
Retronasal olfaction
Nerve circuits involved in taste
The anatomy of taste: from
the tongue (gustatory papillae,
taste buds) to neurons in the
brain via the thalamus
k
mong our five senses, it is
taste that lets us appreciate
dozens of different foodstuffs
Taste
bud may be,
each day. As familiar as
taste
Sulcus
it is far more complex than it appears
at first glance. All the more so since
eating does not just involve one sense
but rather all of them. And taste, as
we understand it in our everyday life,
cannot be simply boiled down to physiology. Putting food in our mouth triggers a whole panoply of sensations: not
only the foodstuff's savor but also its
texture as well as the odors that are
released by chewing it come into play.
All this is referred to as "flavor". And
Salivary
surprise ... The sense of taste
is not
glands
the most important; that distinction is
reserved for the sense of smell.Gustatory
"Threenerve
quarters of sensory perception in the
mouth isAnatomy
down ofto olfaction " attests
Loïc the
Briand
, Inra
Research Director
caliciform
papilla
at the Centre des sciences du goût et
de l’alimentation – CSGA(Centre for
the Sciences of Taste & Diet) in Dijon
"which explains why we can't 'taste'
anything when we have a cold." A cold
impairs the sense of smell because the
mucus blocks the passage of odor via
the back of the nose to receptors on the
olfactory epithelium, a mucous membrane at the top of the nasal cavity that
lets us "smell" odors (see the figure).
Another important component of taste
is that which allows us to experience
the tactile aspect of food and appreciate—or not—the bite of mustard, the
fizz in carbonated drinks, the freshness
of mint, the astringency of tannins in
wine or the heat of chili pepper. These
perceptions are called "trigeminal"
because the signals are transmitted
Nerve circuits involved in taste
©©Olivier AUDY
te
a
olfaction
via the trigeminal nerve that supplies
the face, including the teeth and eyes.
"That's why a strong dose of hot mustard or wasabi makes out eyes water"
explains Loïc Briand. "Taste in the
strictest sense of the word corresponds
to the detection of savors by the gustatory papillae on our tongue. "
Today, five "primary" tastes are recognized. We are all familiar with four
of these, namely sweet, salty, bitter and
acidic. But perhaps less so with the
fifth, umami. Characterized in Japan
Our other senses have taste
Eating is an experience rich in sensations that begins long before the first mouthful. First of all, our appetites are whetted through our eyes: we salivate in advance
when we see an appetizing meal. But simply seeing a foodstuff can likewise make
you feel sick and entail rejection. Next, our sense of touch tells us about the texture of food before we put it into our mouth: hard or soft, elastic. Our hearing
tells us if it is crunchy or crusty. So eating does not only stimulate our senses of
taste and smell but all five senses. All contribute to our brain's image—pleasing
or otherwise—which is generated in the course of this activity that is so important
for our bodies.
at the beginning of the 20 th century,
umami—which translates as "pleasant
savoury taste"—corresponds to the
taste of glutamate, an amino acid that
is one of the basic building blocks of
protein. A common taste in Japanese
cuisine, umami largely comes from soy
sauce and certain types of seaweed,
both of which are extensively used in
Japan. But meat, tomatoes and parmesan cheese also have umami. Above and
beyond pleasure, detecting these basic
tastes is also an important physiological function of the body. "Sweet-tast-
Loïc Briand: UMR6265 CNRS/UMR1324 Inra – Université de
Bourgogne, Centre des sciences du goût et de l’alimentation (Centre for
Sciences of Taste & Diet), Perception de la flaveur (Flavour Perception)
Caliciform
papilla
Foliate
papilla
7
#32
Salivary
glands
The tongue and its papillae
Filiform
papilla
Gustatory
nerve
The tongue and its papillae
Sulcus
Anatomy of
the caliciform papilla
The tongue and its papillae
Fungiform
papilla
©©Olivier AUDY
Caliciform
papilla
Filiform
papilla
Filiform
papilla
Taste bud
Taste bud
Sulcus
Caliciform
papilla
Taste bud
Sulcus
Foliate
papilla
Foliate
Caliciform
papilla
papilla
Foliate
papilla
Salivary
glands
Salivary
glands
Retro
S
Gustatory Gustatory
nerve
g
nerve
Filiform
papilla
Fungiform
papilla
Fungiform
papilla
Fungiform
papilla
ing food signals an energy source that
can be assimilated quickly", explains
Loïc Briand "whereas a bitter taste
could indicate toxicity." For example,
alkaloids like caffeine, nicotine and
cocaine—all of them toxic at high
doses—taste bitter. "Detecting salt is
also important for maintaining
the body's electrolyte balance and
replenishing salt lost through sweating
and urination." Detecting acidity tells
us if fruit is ripe and helps us avoid
spoiled food. Many bacteria generate
acid as they grow, e.g. dairy products
acidify over time because bacteria
found in them produce lactic acid. Finally, umami helps us detect the presence of protein, the only source we
have for nitrogen and the essential
amino acids we need because our bod-
ies cannot produce enough of them.
But how are these tastes recognized?
Thanks to our precious taste buds or
gustatory papillae. Our tongue carry
hundreds of papillae of four different
types: filiform, fungiform, foliate and
circumvallate (see the figure). The first
are the most numerous and give the
tongue its sponge-like texture; these
relay information about the texture of
the food. "Only the last three are called
gustatory papillae and are involved in
taste sensation because they contain
taste buds" says Philippe
Besnard , Professor of Human Nutrition at AgroSup Dijon and director of
the Inserm group at the Université de
Bourgogne. It is our thousands of taste
buds that let us detect the basic tastes.
Their tips come into contact with the
Anatomy of
the caliciform
papilla
Anatomy
of
the caliciform papilla
food and at their base, they feed into
the gustatory nervous
system.
Anatomy
of "Sapid
compounds, i.e. those that carry taste,
the
caliciform
papilla
dissolve in
saliva
and stimulate
membrane-bound receptors at the tips of
the taste buds" explains the scientist.
This stimulation triggers a cascade of
biochemical reactions and ion fluxes
which induce the release of
neurotransmitters at the base of the
receptors. In turn, the neurotransmitters activate gustatory nerves that
transmit the information to the brain.
Then, a number of different parts of
the brain are involved in processing the
Electrolyte balance. Equilibrium between the volume of
water in our body and the minerals it requires to function, such as
sodium, potassium and calcium.
Neurotransmitter. Compound released into a synapse by a
neuron or some other types of cell to transmit a signal to another
neuron.
Philippe Besnard: Inserm Unit 866/EPHE – Université
de Bourgogne, Lipides-Nutrition-Cancer, Physiologie de la nutrition et
toxicologie (Lipids-Nutrition-Cancer, Physiology of Nutrition & Toxicology)
G
n
gustatory signal. Stage 1: the information is processed in the thalamus and
then relayed on to the cerebral cortex
where the taste perception is generated.
Gustatory information is then sent on
to other parts of the brain, notably the
hypothalamus and the hippocampus
that are respectively important in regulating food intake and taste memory.
It was believed for a long time that
different tastes are detected on distinct
parts of the tongue: sugar at the tip, bitter at the base, acidic and salty on the
edges. However, this is wrong. In fact,
every taste bud contains a set of gustatory detectors that respond to all five
primary tastes. "These detectors were
only discovered relatively recently"
points out Loïc Briand. The first were
not reported until the beginning of the
21st century. They are composed of G
protein-coupled receptors (GPCRs),
membrane-bound receptors that elicit
an intracellular response (such as neurotransmitter release) when activated,
in this case by a sapid molecule. "To
date, twenty-five distinct receptors for
bitterness have been identified in humans, as well as one for sweetness and
another one for umami" specifies the
grand angle
k
The five tastes
that are currently
recognized
©©Loïc Briand:
#32
scientist. For salty and acidic tastes,
different types of gustatory detectors
are activated, namely ion channels.
These channels through the cell membrane let pass sodium ions (Na+) from
salty foods pass and hydrogen ions
(H+) from acidic foods.
k In red, fungiform
papillae on the tongue
seen in a scanning
electron microscope
(magnification x63,
6 x 7 cm)
©©Motta/SPL/Phanie
8
The taste of fat
New receptors for the basic tastes may
come to light soon. The scientific community suspects that there may be at
least one more receptor for umami
and probably another for salty. And
even entirely new tastes may soon
be recognized. A taste must fulfill a
number of conditions: "The taste must
be perceptible and unique" stipulates
Loïc Briand "and the stimulus must
induce physiological and behavioral
responses." As described above, sapid
molecules associated with said taste
must activate a specific gustatory detector which in turn triggers the release
of a signal that is transmitted via the
gustatory nerves. Possible new tastes
include that of "fat". Until recently,
lipids were considered as tasteless or
insipid, their appeal deriving simply
from their texture and smell. However,
recent work in rodents and humans
suggest that "fat" is probably an entirely distinct taste. Everything started
with the discovery of a receptor for
lipid called CD36 (cluster of differentiation 36) in the gustatory papillae
of the rat. "It is known to play a role
in the gut, notably in the assimilation
of lipid" says Philippe Besnard, whose
research focuses on the metabolism of
dietary fat. What does this receptor
do in the papillae? This is one of the
questions Besnard's group is seeking
#32
Rosa at the Institute of Biology of the
to answer. They first showed that this
receptor is found on sensory cells in the
taste buds of mice. "Then we showed
that mice in which the CD36 gene had
been knocked out no longer preferred
the lipid when offered a choice between
a lipid-rich solution and a control solution." They also showed that the presence of lipid in the mouth induces the
release of neuromediators from taste
buds towards gustatory nerves. The
murine gustatory system is therefore
fully equipped to detect lipid. Other
experiments in Philippe Besnard's
laboratory have shown that lipid induces a physiological response in mice,
e.g. the presence of lipid in the mouth
triggers the secretion of bile salts by
the liver, and of digestive enzymes by
the pancreas, even in the absence of
any ingestion. It is now established
that CD36 is also found on the gustatory cells of humans and many other
mammals. The work of Richard Mattes
and his team at Purdue University in
the United States recently showed that
humans can distinguish the taste of
"fat", which they named oleogustus,
from the other primary tastes. So can
"fat" be considered as the sixth primary taste? "The groundwork has been
accomplished in rodents and evidence
is building in humans" judges Philippe
Besnard. Being able to taste fat would
make sense from a physiological point
©©Inserm/ Patrice Latron
k
The Inserm LipidsNutrition-Cancer group
studies the metabolism of
dietary lipid in mice.
Paris École Normale Supérieure have
shown that consuming bitter and acidic
food induces the expression of a specific gene, Egr-1, in Zebrafish larvae.
"The gustatory system works similarly
in most living organisms" points out
Brigitte Boyer. Being able to identify
foodstuffs and evaluate their nutritional composition would represent a
selective advantage that would have
appeared very early in the course of
evolution. It is therefore reasonable—
to some extent—to extrapolate findings in other species like the Zebrafish
to human beings. The Egr-1 gene encodes an early transcription factor that
regulates the expression of other genes.
Experiments in mice have shown that it
is involved in memory. "We believe that
Egr-1 is involved in the memorization
of tastes and therefore in the gustatory
learning process" explains the biologist, "because progressive habituation
of view: lipid-rich food is not only a
of the young fish to bitter and acidic
very good source of energy, but it is
tastes as a result of repeated exposure
also likely to contain essential fatty
is accompanied by lowering of the exacids like the omega-3 series as well
pression of Egr-1." Dietary preferences
as important vitamins (A, D, E and K).
are therefore to
And the purpose
some extent writof taste is to identen in our genes.
tify foodstuffs that
"The gustatory system
But preferences are
provide the best
works similarly in most
dynamic and evolve
nourishment. It also
according to our
helps us link first
living organisms"
experiences.
contacts with our
To investigate chilenvironment.
dren's dietary preferences and how
they change, a number of groups from
How does taste change?
a variety of disciplines (biology, medicine, psychology, sociology, ethology,
The gustatory system develops very
statistics, etc.) came together in 2005
early on in utero. Gustatory papillae
to assemble a cohort called Opaline
appear before the end of the first trimester of pregnancy and it is believed
(Observatoire des préférences alimenthat the fetus can sense tastes present
in the amniotic fluid by the third trimester. Work by Benoist Schaal, CNRS
Benoist Schaal: UMR6265 CNRS/UMR1324 Inra – Université
Research Director at the Dijon Centre
de Bourgogne, Centre des sciences du goût et de l’alimentation (Centre for
Sciences of Taste & Diet), Perception de la flaveur (Flavour Perception)
for the Sciences of Taste & Diet, has
shown that new-born babies are atBrigitte Boyer, Frédéric Rosa: Inserm Unit 1024/
CNRS – École normale supérieure Paris, IBENS, Early Development
tracted by the smell of aniseed if their
mother regularly ate this kind of sweet
F. Laugerette et al. Journal of Clinical Investigation, 1 November 2005;
in the last two weeks of pregnancy. So
115 (11): 3177-84
the first experiences of tasting occur
D. Gaillard et al. The FASEB Journal, May 2008; 22 (5): 1458-68
in the mother's womb. At birth, babies
C. A. Running et al. Chemical Senses, September 2015; 40 (7): 507-16
have an innate preference for sugar and
B. Schaal et al. Chemical Senses, December 2000; 25 (6): 729-37
instinctively reject bitter and acidic
foods. This could have a genetic basis.
B. Boyer et al. Frontiers in behavioral neuroscience, 22 May 2013; 7: 51
Work by Brigitte Boyer and Frédéric
9
grand angle
#32
Sophie Nicklaus: UMR6265 CNRS/UMR1324 Inra – Université
de Bourgogne, Centre des sciences du goût et de l’alimentation,
Développement et dynamique des préférences et des comportements
alimentaires (Centre for Sciences of Taste & Diet, Development & Dynamics
of Eating Preferences & Habits)
C. Schwartz et al. British Journal of Nutrition, November 2009;
102 (9): 1375-85
C. Schwartz et al. British Journal of Nutrition, March 2013; 109 (6):
1154-61
C. Schwartz et al. Physiology & Behavior, 26 September 2011;
104 (4): 646-52
Breast feeding
encourages a liking for
umami.
k
k
Dietary diversification
is a key phase of learning
about taste.
"Children who like
vegetables when they first
taste them still like them at
two"
children readily accept new foodstuffs.
Thus, between five and seven months,
the reactions of 88% of children to
new foods were judged positive.
Familiarity breeds liking
Vegetables are usually what children
like least—and what they eat least.
Even though they are healthy by virtue of the vitamins, minerals and fiber
that they contain. To determine what
influences children's eating habits and
thereby help parents with practical
guidelines, the work on the Opaline
cohort addressed how taste for unloved
vegetables changes. Based on data collected from volunteers, the statisticians
detected significant links between preferences at the beginning of weaning
and the situation at two years of age.
"Children who like vegetables when
they first taste them still like them at
©©Africa studio/Fotolia
taires du nourrisson et de l’enfant, Observatory of the Dietary Preferences of
Babies & Children). This longitudinal
study being sponsored by Inra, CNRS
and Inserm followed 319 mother-andchild pairs from the Dijon area from
the end of pregnancy until the child
reached the age of two. "We set out
to determine their dietary experience
and sensory exposure in depth" states
Sophie Nicklaus, Inra Research Director at the Dijon Centre for the Sciences
of Taste & Diet and Head of the Opaline Steering Committee. Comprehensive data were collected on the foods
consumed by the mother during pregnancy, the duration of breast feeding,
the variety of foods and preparations
introduced at weaning and the dates
when salt, fat and sugar were added.
Laboratory tests were also carried out
to investigate the babies' preferences
vis-a-vis the five primary tastes. By
comparing water consumption with
that of a sapid solution (sweet, salty,
acidic, bitter or umami), these tests
confirmed that the first taste that babies like is sweet. Milk—be it breast
milk of formula—is slightly sweetened.
The taste for salt develops between
four and six months, around the time
of weaning, and grows over the first
year. On the other hand, reactions to
umami are usually neutral. "But we
observed that prolonged, exclusive
breast feeding is associated with a liking for the umami taste by six months"
adds Sophie Nicklaus. This is probably
due to the fact that breast milk is very
rich in glutamate, the amino acid that
underlies this taste. As for acidic and
bitter, these are the least popular tastes,
although they are not completely rejected by children of the ages studied.
Preferences for certain tastes affect
young children's eating habits but only
to a certain extent: at weaning, most
©©Muro/Fotolia
10
two" she says. However, no association
was observed between the vegetables
consumed by the pregnant mothers
and their child's preferences. Nor
does the duration of breast feeding
seem to have any effect, in contrast
to the conclusions of some previous
studies. Conversely, "Variety of vegetables and recipes has a strong effect
on a child's preferences at the time of
weaning" continues Sophie Nicklaus.
In the same way as the Zebrafish gets
used to bitterness, repeated exposure
to vegetables promotes acceptance: an
effective, reproducible way of guiding
the learning process. "A baby may be
offered a foodstuff eight, ten or even
fifteen times before it is accepted but,
in the end, it usually is. "
Getting to like a new foodstuff is a
learning process. The influence of education on liking for vegetables was
also studied. Two parental practices
#32
were associated with the consumption of less vegetables by the age of
two. "Offering something else when
a child refuses a new foodstuff will
limit his or her exposure to varying
tastes" explains Sophie Nicklaus. "The
child will never learn to like the new
foodstuff." Similarly, forcing a child
to clear the plate creates a prejudicial
atmosphere when it comes to liking
food, vegetables in particular. "It is
important to favor exposure and introduce variety by changing recipes, but
without forcing the child to eat" concludes the scientist. "The pleasure of
tasting is fundamental during this key
period when it comes to dietary preferences." This is the period of life when
neophobia—rejection of any new foodstuff—can become installed in a child.
And previous work by Sophie Nicklaus
for her doctorate had demonstrated
significant links between dietary habits
acquired in young childhood and those
at the beginning of adulthood.
11
ogy seems to play an important role.
"They tend to eat under the influence
of their emotions and prefer sweet and
fatty-sweet products" adds Caroline
Méjean. Socio-economic status
is also important, with those on low
incomes generally having a stronger
liking for fat than the better-off.
Cheaper food tends to be less healthy,
largely because specific types of fat are
often added to processed products to
enhance their taste. And "the more fat
you eat, the more you are attracted to
collected and analyzed by Aurélie Lampuré, a doctoral student working with
Caroline Méjean, identified a series of
specific profiles, especially concerning
likings for fatty-salty and fatty-sweet
food. First determinant observed: gender. Men tend to prefer fatty-salty food
whereas women seem to prefer fattysweet. "Men seem to let themselves be
guided by their sensory likings that
generally drive them towards consuming more fatty-salty products" explains
the epidemiologist. In women, psychol-
Gender is the most
important determinant of
liking for fatty-salty and
fatty-sweet foods
k
NutriNet-Santé study. Cohort study started in 2009,
focusing on the dietary habits of a large population of Internetusing adults (in June 2016, there were 274,011 on-line subjects)
followed for at least five years to investigate relationships
between nutrition and health.
www.etude-nutrinet-sante.fr
Caroline Méjean: Inserm Unit 1153/Inra/Université Paris 13-
Paris Nord/Université Paris 7-Denis Diderot – Université Paris-Descartes,
CRESS, EREN
S. Bouhlal et al. Appetite, 1 December 2014; 83: 209-17
S. Nicklaus, Étude longitudinale des préférences et de la variété
alimentaire de la petite enfance jusqu’à l’âge adulte : choix des enfants de
2 à 3 ans et lien avec leur comportement de 4 à 22 ans. (Longitudinal study
of preferences and dietary variety from young childhood through adulthood:
choices of 2-3 year-old children and their behavior from 4 to 22 years of
age) Dissertation for a doctorate in Food Science defended at the Université
de Bourgogne in 2004
©©NutriNet-Santé
In the young, dietary preferences therefore have their roots in young childhood and family history. But in adults?
"Most of the data available are experimental and confined to some specific, relatively homogenous
population" says Caroline Méjean, Inra
scientist at the Sorbonne Paris Cité
Centre for Research in Epidemiology
& Statistics (CRESS). However, taste
is the most important parameter when
it comes to making dietary choices.
Sensory determinants are a major factor in our behavioral patterns vis-a-vis
eating. To mitigate the lack of
<data, Investigators from the
NutriNet-Santé study are working
with a cohort of volunteer Internet
users helping to shed light on the eating
habits of the French and Belgian populations. The aim is to identify population characteristics associated with
sensory attraction. A total of
37,181 surfers filled out a scientifically
validated questionnaire about their
dietary preferences for fatty, salty and
sweet foods. These volunteers also gave
details on what they ate and drank over
three days, as well as how much. Data
©©Michael Donne/SPL/Phanie
Fatty-salty or fattysweet?
S. Nicklaus et al. Appetite, June 2005; 44 (3): 289-97
S. Nicklaus et al. Food Quality and Preference, October 2004; 15 (7-8):
805-18
A. Lampuré et al. British Journal of Nutrition, October 2014; 112 (8):
1353-63
A. Lampuré et al. The Journal of Nutrition, 1 March 2015; 145 (3): 587-94
12
#32
grand angle
However, these broad findings cover
substantial variation between different individuals. "Some inter-individual
variability is due to genetic polymorphism" explains Loïc Briand. For example, some 2% of people do not sense
the umami taste of glutamate. In this
form of impaired taste function (or
partial ageusia), a number of polymorphisms—different variants of a given
gene—influencing how the umami
receptor works have been shown to
play a role in work which Loïc Briand
contributed to. Similarly, some 30%
of the population is insensitive to
phenylthiocarbamide, a bitter-tasting
compound found in many green vegetables, including broccoli and Brussels
sprouts. These "non-tasters" are more
likely to like these vegetables because
they do not find them so bitter. Conversely, there are "super-tasters" who
are particularly sensitive to bitterness.
And the same goes for sugar: "Sensitivity to sweetness can vary by a factor
of ten from one person to another"
confirms Loïc Briand.
k Tastes vary! A given
©©Olly/Fotolia
dish will not taste the
same to everyone.
fatty foods" she says. Lifestyle is important too: smokers and heavy drinkers tend to prefer fatty-salty food.
"Smoking and drinking impair taste
sensation" specifies Caroline Méjean.
"So these people tend to consume
larger quantities of fatty-salty products
to get the same sensation as non-smokers or light drinkers." Finally, data collected for this study also indicate that
taste for both fat and sugar wanes with
age. "It is possible that, as one gets
older, one becomes more aware of the
impact of nutrition on health" proposes Caroline Méjean. "And this
"The more fat you eat,
the more you are attracted
to fatty foods"
Taste governs our diet
We do not all perceive all tastes in the
same way. Some prefer sweet, others
savory... and this will be reflected in
what they eat. And what we eat has
direct impact on our health. Poor diet
(see Box on page 33) is associated with
an increased risk of cancer, cardiovascular disease, obesity and diabetes.
Could our taste make us sick? At least
in part, according to some findings.
For instance, Caroline Méjean and
her team have shown that the dietary
profile of volunteers in the NutriNetSanté study who are most attracted by
fatty foods is less healthy from a nutritional point of view. "They ingest more
calories from meat, fat and sugar"
stipulates Caroline Méjean "and in
parallel, they do not eat much fruit,
vegetables or fish. "With all the longterm health consequences that go with
that. In a recent longitudinal study, her
team looked at how fondness for fat
is related to the prevalence of obesity.
would tend to lead to a more balanced
diet." Eventually, eating less fat and
sugar leads to a reduced desire for such
foods. It is also possible that this agerelated effect could be due to reduced
physiological sensitivity to tastes and
smells.
k
©©Loïc Briand
Japanese display of
foodstuffs rich in the taste
of umami (shrimp, dried
seafood, etc.)
O. Lugaz et al. Chemical Senses, February 2002; 27 (2): 105-15
M. Raliou et al. Chemical Senses, July 2011; 36 (6): 527-37
13
#32
A genuinely "gentle"
drug
Other experiments are also showing
that obese mice are less sensitive to
sweet things, and that the same phenomenon can be observed in humans.
However here too, scientists do not all
agree. Although sugar never comes out
whiter than white. It is believed to be
Nutritional balance in a logo
What is a balanced diet? It means eating enough healthy, varied foodstuffs to
meet our energy needs and keep us in good health. To encourage people to eat a
balanced diet, French public agencies established the Programme national nutrition santé (PNNS, National Nutrition &
Health Program) in 2001*. Its recommendations include eating at least five fruits
and vegetables a day as well as cutting
down intake of salt, sugar and fat. To
encourage choice of more "nutritionally" desirable foods, a labeling system
for commercially available products is
being set up. This will make it possible
to compare the nutritional quality of
similar products by means of a simple
logo. However, this will not take into account what the product tastes like. "Such
a labeling system will push companies
to improve their products' nutritional
quality by cutting down their fat, salt
and sugar content" notes Serge Hercberg, President of PNNS, Professor of
Nutrition at Paris 13 Medical School and
Inserm Research Director in Nutritional
Epidemiology, which should eventually
reduce intake of these nutrients and help
wean consumers off from these tastes. "
www.mangerbouger.fr
* See S&S # 26, In the headlines, "PNNS begins to yield
fruit", p. 4-5
addictive and playing a central role in
the explosion of metabolic diseases like
diabetes and obesity in our societies of
dietary abundance**. "Addiction is a
behavioral problem that undermines
control of how much of something is
consumed" explains Serge Ahmed, Director of a CNRS team at the Institut
des maladies neurodégénératives
(IMN) (Institute of Neurodegenerative
Disease in Bordeaux) and specialist in
pathological addiction. It is usually associated with drugs such as heroin and
cocaine or nicotine and alcohol. The
consumption of such drugs activates
neurons in the reward circuit that release dopamine in the brain. "Release
of this neurotransmitter rewards the
behavior that induced its release, in
this case taking the drug" the scientist
goes on. "This reinforcement then
drives some people to take it again and
again in a pathological pattern." Could
©©Monkey Business/ Fotolia
Data from questionnaires filled out
by 24,776 adults from the NutriNetSanté cohort show that a taste for fat
is associated with a higher risk of becoming obese within five years: people
who like fat eat a less healthy diet than
those who do not like it as much.
According to this epidemiological
survey, a taste for "fat" is associated
with a poorly balanced diet which ultimately raises the risk of obesity. But
once it is installed, does obesity in turn
affect taste, notably that for fat? The
answer is apparently yes according to
experiments in mice carried out by
Philippe Besnard. "Obese mice detect
ingested lipid less effectively than mice
of normal weight" he states. This lack
of sensitivity leads to more frequent
eating in these animals. "These rodents
probably have to eat more lipids to get
the same gustatory gratification—referred to as the hedonistic threshold"
explains the scientist. This work has
also shown that the CD36 lipid receptor does not work properly in these
obese mice, similar to what is seen in
mice in which this receptor has been
knocked out (see page 29). "This finding confirms how important this receptor is in lipid detection." However,
this loss of sensitivity can be reversed
by feeding the mice a low-calorie diet:
as the obese mice lose weight, their
perception of lipid intake steadily improves. Obesity would seem therefore
to be the cause of the dysregulation in
mice. But what about humans? "Work
on lipid detection in obese subjects has
given contradictory results, sometimes
causing controversy" regrets Philippe
Besnard. Still, gustatory tests carried
out by his team and that of Sophie
Nicklaus have shown that the detection
of certain lipids is perturbed in these
subjects compared with this function
in slim people.
Serge Hercberg: Inserm Unit 1153/Inra/Université
Paris 13-Paris Nord/Université Paris 7 – Denis Diderot –
Université Paris-Descartes, CRESS, EREN
certain foodstuffs sometimes act like a
recreational drug? "Extrapolating the
criteria that define addiction to foodstuffs, 5 to 10% of people of normal
weight display addictive behavioral
patterns to food " proposes Serge
Ahmed "and this proportion rises with
body mass index, reaching 40% in
obese people." And many foods that
Serge Ahmed: UMRS293 CNRS, Université de Bordeaux,
IMN, Prise de décision pathologique de l’addiction (Decision-making in
pathological addiction)
** See S&S # 25, Opinions, "Sugar addiction: reality or myth?",
p. 40-41
C. Méjean et al. Appetite, 1 July 2014; 78: 147-55
A. Lampuré et al. International Journal of Nutritional Behavior and
Physical Activity, 4 July 2016; 13: 74
M. Chevrot et al. Journal of Lipid Research, September 2013; 54 (9):
2485-94
M. Chevrot et al. The American Journal of Clinical Nutrition, 1
May 2014; 99 (5): 975-83
#32
Dopamine. Neurotransmitter secreted by dopaminergic
neurons (which are mainly involved in controlling motility and in
the reward system).
Body Mass Index (BMI). Parameter that estimates an
adult's corpulence, calculated by dividing weight in kilograms
by the square of height in meters. A BMI of between 18 and 25
corresponds to normal corpulence. Someone with a BMI of over
30 is considered as obese.
E3N cohort. Prospective cohort study launched in 1990
covering about 100,000 French women born between 1925
and 1950 affiliated with the National Education Mutual Insurance
System.
www.e3n.fr
Guy Fagherazzi: Inserm Unit 1018/Université Versailles-Saint-
Quentin-en-Yvelines – Université Paris-Sud 11, Centre de recherche en
épidémiologie et santé des populations (Center of Research into Population
Epidemiology & Health)
M. Lenoir, F. Serre et al. PLoS One, 1 August 2007; 2 (8): e698
G. Fagherazzi et al. The American Journal of Clinical Nutrition,
March 2013; 97 (3): 517-23
Experiment to assess sugar's addictive
potential. The rat can press on a lever to get a
sweet drink. It is also connected to a system
that administers an injection of cocaine.
The animal can choose between these two
substances.
k
some people claim to be addicted to—
fizzy drinks, ice cream, chocolate—
contain sugar—a great deal of it.
However, not everyone who likes these
products is a junkie. "The same is true
of recreational drugs" explains Serge
Ahmed. "It is estimated that one in
three smokers are dependent; and with
alcohol, the proportion is one in
ten." Addictive potential thus depends
on the substance. To compare the addictive potential of sugar with that of
cocaine, Serge Ahmed subjected rats to
a dual choice test: the animals could
choose between a sweet drink and an
injection of cocaine. Results: 85% of
the rats preferred the sweet drink. So
in rats, sugar seems to be more addictive than cocaine. Such findings can
obviously not be directly extrapolated
to human beings but they do show that
the addictive potential of sugar is real.
More than other foodstuffs? "We think
that the addictive potential of sugar is
largely due to what it does in the brain"
proposes the scientist. "Unlike other
nutrients, the glucose in sugar directly
interacts with the brain's reward circuit." But sugar's addictive potential
remains a controversial subject. Of
course, industrial lobby groups raise
doubts but the same is true of some
voices in the scientific community who
point to the lack of evidence that there
is such a thing as sugar tolerance. And
tolerance—the need to consume more
and more of something to obtain the
grand angle
©Eric Augier
14
same degree of gratification—is usually considered as a necessary characteristic of addiction to a substance.
No more sugar
substitutes
natural sugar. They could even
be worse. A recent epidemiological
Artificial sweeteners like aspartame
survey of a sample of 66,118 women
make food sweet without all the caloin the E3N cohort conducted by
ries of sugar; could these be part of the
Guy Fagherazzi, an Inserm researcher
solution to the possibility of sugar adat Gustave-Roussy in Villejuif, showed
diction? "In theory,
that artificially
yes" answers Serge
sweetened lite
Ahmed. But drinkdrinks are associ"Artificial sweeteners
ing artificially
ated with a higher
activate sugar receptors risk of diabetes
sweetened drinks is
often associated
than drinks conin the gut"
taining regular
with the consumption of sugar in
sugar. To cut down
other forms which ultimately mainglucose absorption in the gut, comtains a craving for sugar." Moreover,
pounds that inhibit these receptors
receptors that mediate the taste of
could be developed for therapy. "Plants
sweetness are not only found on the
used in ayurvedic medicine like
tongue but also in many other tissues
Gymnema sylvestre contain such inhibitory substances, in this case gymnelike the small intestine, colon, pancreas
mic acid" notes Loïc Briand. "They
and brain. And "synthetic sweeteners
have long been used in this ancient Inactivate these receptors in the gut to
dian medical practice to lower glucose
promote the absorption of glucose into
levels in the blood of diabetics." Howthe blood" points out Loïc Briand. So
ever, scientific evidence of their theraartificial sweeteners affect glycaemia
peutic benefits remains restricted to just
(the concentration of glucose in the
a few clinical trials.
blood) and could be as guilty in the
Just like likings for fat and sugar, a taste
development of diabetes mellitus as
#32
for salt may also have health consequences. Salt tends to raise blood pressure. Hypertension is associated with a
risk of cardiovascular disease, especially
stroke and, to a lesser extent, myocardial infarction . And according to
the results of the NutriNet-Santé study,
the French are eating too much salt:
8.4 grams a day on average while the
World Health Organization recommends a maximum of 5 grams; 2% of
volunteers systematically put salt on
their food before tasting it and 8% declare doing so on a regular basis. Hypertension due to excess salt can
nevertheless be reversed by consuming
a low-salt diet which gradually reduces
cravings for salty food. Salty food can
even become unpleasant-tasting, leading to a permanent feeling of thirst. The
attraction of different foods—salty or
not—is therefore not static; it can
change with a change in diet.
Taste rehab
Our senses can help us learn or relearn how to taste. Sensory education
gain. A recent study of 52,163 volunteers from the NutriNet-Santé cohort
just detected a significant link between
intuitive eating and weight: people who
only eat when they feel hungry (rather
than in response to emotion) and stop
eating once they feel full are less likely
to be overweight or obese. Taste could
therefore be made an ally in the fight
against many dietary problems, making it possible to find or restore the
pleasure of healthy eating. n
k
Patient consulting a dietitian at a
hospital specializing in the treatment
of obesity in children and teenagers
is a therapeutic tool used to treat certain metabolic problems like obesity,
against which it can be more effective
than serially repeated dieting. "Intuitive eating" is one of the methods based
on sensory education. "The principle
is not to ban any foodstuff but to restrict the amount consumed and, at the
same time, enhance the pleasure associated with eating it, notably by eating
it slowly" specifies Dr DominiqueAdèle Cassuto, endocrinologist and
nutritionist, who uses it on groups of
obese teenagers at La Pitié-Salpêtrière
Hospital in Paris. A preliminary phase
consists of helping patients put words
on their relationship with food and
then helping them to get used to feelings of hunger and satiety by listening
to their bodies. Then they attend tasting workshops to restore the sensory
aspects of eating; not only taste but
also the other senses. And the results
can be surprising. "The teenagers' attitudes to food change." celebrates the
nutritionist. "They come to realize that
'little' and 'good'' can be enough to
satisfy." Which checks their weight
Find the
Saveurs & Santé
(Tastes and Health) Train
from 5-23 October 2016
at any of its 15 stops.
©©AJ PHOTO/HPR BULLION/SPL/Phanie
www.inserm.fr
Stroke. Obstruction or bursting of a blood vessel in the brain
that causes the death of nerve cells.
Myocardial infarction/ A "heart attack" is characterized by
the death of heart muscle cells in an area of variable size.
G. M. Camilleri et al. Obesity, May 2016; 24 (5): 1154-61
15
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